CHEYENNE, Wyo. (AP) -- An undercover probe of a pig farm near Wheatland by the Humane Society of the United States has resulted in misdemeanor charges against nine former workers.

The Platte County Attorney's Office filed the charges in recent weeks. Officials are still attempting to serve some defendants.

The Humane Society last summer released what it said is an undercover video, shot in April, showing workers abusing pigs at Wyoming Premium Farms in Wheatland. The society also claimed animals at the farm were kept in what it called inhumane conditions.

"The Humane Society of the United States applauds the Wyoming Livestock Board and the Platte County Attorney's Office for their serious attention to cruelty to animals, including animals raised for food," said Adam Parascandola, director of animal cruelty response for the Humane Society.

Attempts to reach Platte County Attorney Eric Jones for comment were unsuccessful. His office said Wednesday he has a policy of not commenting on pending cases.

Livestock Board Director Leanne Correll was unavailable for comment, her office said Wednesday. The board investigated the complaint from the Humane Society.

The nine defendants face from two to seven misdemeanor counts each of cruelty to animals. The charges are based on sworn statements from a Humane Society worker who claims she witnessed mistreatment.

Attempts to reach defendants for comment were unsuccessful on Wednesday.

The Clerk's Office at the Platte County Circuit Court said all the defendants are scheduled to have a first appearance next month and that none has filed notice that they've retained an attorney.

Dr. Jason Hocker, a veterinarian with AMVC Management Services in Audubon, Iowa, said Wednesday that Wyoming Premium Farms hired his company in June 2012. He said a comprehensive swine welfare and handling training program was put into place that month and that the defendants are no longer working at the farm.

"Wyoming Premium Farms is committed to raising pigs in a healthy and humane manner and supplying pork to feed a growing global population," Hocker said in a statement, adding that the company fully supports accountability for anyone working with animals.